Small particle copper pyrithione

ABSTRACT

Disclosed herein is a composition comprising a non-dusting copper pyrithione dispersion comprising small solid particles of copper pyrithione dispersed in a liquid dispersant, said solid particles having a particle size within a range of from about 0.1 to about 10 microns and a median particle size of less than 3 microns. The dispersion is suitably employed as an antifouling additive for marine paints without risking worker exposure to copper pyrithione dust. Paints containing the small particle copper pyrithione exhibit improved antifouling performance in cold water, as compared to paint containing larger particle copper pyrithione.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to small particle copperpyrithione compositions, and a method of preparing these compositions.Preferably the compositions are provided in a non-dusting form as adispersion of the small particles in an aqueous or organic solventcarrier. Alternatively, the small particles are provided in the form ofa solid powder for use in facilities equipped to avoid or minimize humanexposure to, and handling of, the powder. The small particle copperpyrithione compositions are suitable for use as antifouling agents inantifouling paints, such as marine paints. These small particles exhibitenhanced storage stability in dispersions with liquid media, as well asan enhanced leach rate from the antifouling paints, relative to largersize copper pyrithione particles.

2. Description of the Related Art

Pyrithione salts are well known compounds that are useful in a widevariety of applications including their use biocides, such as fungicidesand bactericides. Heavy metal salts of pyrithione, including zinc, tin,cadmium and zirconium, as well as the magnesium and aluminum salts, havebeen produced in the form of flat platelets suitable for use in shampoo,are disclosed in U.S. Pat. Nos. 4,345,080 and 4,323,683.

Small particles of metal salts of pyrithione have been disclosed for useon the skin and hair. Illustratively, U.S. Pat. No. 4,670,430 disclosespolyvalent metal salts of 2-mercaptopyridine-N-oxide in the form of afine powder of particles in which at least fifty percent of theparticles have a particle size below 0.2 micron. The '430 patentdiscloses that, when this fine particle of particles is incorporatedinto shampoo or rinse compositions, the dispersion stability of thesesalts is improved and the adsorbability of the particles onto the skinand hair is enhanced. Another illustration of the use of small particlesof metal pyrithiones in hair treatment is provided in U.S. Pat. No.5,723,112. The '112 patent discloses an antimicrobial hair treatmentcomposition comprising (a) a surfactant, (b) fine particles of aninsoluble particulate metal pyrithione in which at least 90% by weightof the particles have a size of five microns or less, and (c) apolymeric cationic deposition aid for the small particles.

Pyrithiones have also been used as antimicrobial additives in a varietyof paints. Illustratively, various paints containing a pyrithione salt(e.g. zinc or sodium pyrithione) plus a copper salt (e.g. cuprous oxideor cuprous thiocyanate) are known in the art, as disclosed, for example,in U.S. Pat. No. 5,057,153. As another illustration, U.S. Pat. No.5,185,033 describes a process for making a paint or paint basecontaining copper pyrithione or pyrithione disulfide plus cuprous oxide,wherein the paint exhibits stability against gelation during storage. Asyet another illustration, U.S. Pat. No. 5,246,489 discloses a processfor providing in situ generation of copper pyrithione in a paint orpaint base which comprises incorporating a metal salt of pyrithione,cuprous oxide and a controlled amount of water into the paint eitherduring or after the formation of the paint.

In many applications, copper pyrithione offers several advantages overother forms of pyrithione such as zinc pyrithione. For example, copperpyrithione is more stable than zinc pyrithione when added to paintproducts, and therefore is less likely to cause gelation during storage.

Commercially available copper pyrithione is typically sold as a drypowder. Generally, the particle size range for this commercial drypowder is between about 0.8 micron and about 30 microns, with a medianparticle size of from 3 to 6 microns. A key disadvantage of thiscommercial powder is that it generates dust during handling,necessitating special handling equipment, particularly since copperpyrithione powder was shown to be more toxic than zinc pyrithione powderwhen tested for acute inhalation toxicity in rats. This dusting issueassociated with copper pyrithione dry powder is addressed in PCTpublication WO00/54589. This publication discloses resolving the dustingissue using dispersions of solid copper pyrithione in a liquiddispersing medium.

The present inventors have now observed that, in use, although thedispersions of the PCT publication WO00/54589 obviate the dusting issue,they are subject to another problem. More specifically, paints made withthese dispersions tend to provide a decreased leaching rate of copperpyrithione out of the paint in a low temperature environment. Suchdecreased leaching increases the likelihood that not enough antifoulingagent will leach from the paint to prevent marine fouling at the paint'ssurface. The present invention provides one solution to this decreasedleach rate problem, thereby insuring desired low temperature antifoulingefficacy for copper pyrithione-containing antifouling paints.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a composition comprisingsmall particles of copper pyrithione having a particle size within arange of from about 0.1 to about 10 microns, and a median particle sizeof less than 3 microns, these small particles exhibit enhancedantimicrobial performance, as compared to larger size copper pyrithioneparticles, in a marine paint that is exposed to a cold water environmentof from about 5 degrees Centigrade to about 15 degrees Centigrade. Inanother aspect, the invention relates to a paint containing the smallparticles of copper pyrithione. In another aspect, the invention relatesto a method for enhancing the antifouling efficacy of a paint in a coldwater environment, said method comprising incorporating the smallparticles of pyrithione into the paint.

In another aspect, the present invention relates to a compositioncomprising a non-dusting copper pyrithione dispersion comprising smallsolid particles of copper pyrithione dispersed in a liquid dispersant.Preferably, the solid particles have a particle size within a range offrom about 0.1 to about 10 microns, and a median particle size of lessthan 3 microns. Optionally, the dispersion additionally contains adust-inhibiting agent selected from the group consisting of surfactants,polymer resins, binders, and combinations thereof.

In another aspect, the present invention relates to a method of making anon-dusting dispersion of small solid particles of copper pyrithionedispersed in a liquid dispersant comprising the steps of:

(a) providing small solid particles of copper pyrithione within adesired size range of from about 0.1 to about 10 microns, and a medianparticle size of less than 3 microns, by subjecting larger solidparticles of copper pyrithione to a force selected from the groupconsisting of grinding, milling, pulverizing, sonicating, andcombinations thereof, and

(b) dispersing copper pyrithione particles in a liquid dispersant.

In yet another aspect, the present invention relates to a method ofmaking a non-dusting dispersion of small solid particles of copperpyrithione dispersed in a liquid dispersant comprising the steps of:

(a) dispersing larger solid particles of copper pyrithione in a liquiddispersant to provide a liquid dispersion have said larger solidparticles dispersed therein, and

(b) subjecting said liquid dispersion of copper pyrithione to a forceselected from the group consisting of grinding, milling, pulverizing,sonicating, and combinations thereof, in order to reduce the size ofsaid larger size particles in said dispersion within a desired sizerange of from about 0.1 to about 10 microns, and a median particle sizeof less than 3 microns.

In still another aspect, the present invention relates to a method ofenhancing the antifouling characteristics of a paint which comprisesadding to the paint an antifouling effective amount of solid particlesof copper pyrithione having a particle size within a range of from about0.1 to about 10 microns, and a median particle size of less than 3.0microns.

In yet another aspect, the present invention relates to a method ofenhancing the antifouling characteristics of a paint which comprisesadding to the paint an antifouling effective amount of a non-dustingcopper pyrithione dispersion comprising small solid particles of copperpyrithione dispersed in a liquid dispersant, said solid particles havinga particle size within a range of from about 0.1 to about 10 microns,and a median particle size of less than 3.0 microns.

In still another aspect, the present invention relates to an antifoulingpaint comprising a paint base and an antifouling effective amount solidparticles of copper pyrithione having a particle size within a range offrom about 0.1 to about 10 microns, and a median particle size of lessthan 3.0 microns.

In yet another aspect, the present invention relates to an antifoulingpaint comprising a paint base and an antifouling effective amount solidparticles of copper pyrithione having a particle size within a range offrom about 0.25 to about 7 microns, and a median particle size of lessthan 2 microns.

In still another aspect, the present invention relates to a method ofenhancing, in a cold water marine environment, the leach rate of copperpyrithione from a copper pyrithione-containing paint, said methodcomprising incorporating into the paint solid particles of copperpyrithione having a particle size within a range of from about 0.1 toabout 10 microns and a median particle size of less than 3 microns, inorder to provide a copper pyrithione leach rate from the paint of atleast one microgram per square centimeter per day of exposure of saidpaint to said cold water marine environment when measured at a coldwater temperature of 10.6 degrees Centigrade.

In yet another aspect, the present invention relates to a copperpyrithione-containing antifouling paint providing an enhanced rate ofleaching of the copper pyrithione from the paint in a cold water marineenvironment, said paint comprising a paint base and an antifoulingeffective amount of solid particles of the copper pyrithione, said solidparticles having a particle size within a range of from about 0.1 toabout 10 microns, and a median particle size of less than 3 microns,said solid particles having a leach rate from the paint of at least onemicrogram per square centimeter per day of exposure of said paint tosaid cold water marine environment when measured at a cold watertemperature of 10.6 degrees Centigrade.

These and other aspects of the present invention, will become apparentupon reading the following detailed description of the invention.

DESCRIPTION OF DRAWING

FIG. 1 is a graph showing the impact of particle size and temperature onthe leach rate of copper pyrithione from paints, over time on a paint ofthe present invention (Paint 4) as compared to comparison paints (Paints2 and 3).

DETAILED DESCRIPTION OF THE INVENTION

It has now been surprisingly found by the present inventors that smallparticles of copper pyrithione exhibit an enhanced leach rate fromantifouling paints containing these small particles, notably in a coldwater environment. This enhanced leach rate enhances the antifoulingefficacy of the paint in that environment, as compared to paintcontaining larger size copper pyrithione particles.

As used herein, the term “cold water environment” denotes a watertemperature of from about 5 degrees Centigrade to about 15 degreesCentigrade. As used herein the terms “small size” and “small solid”, asused in reference to copper pyrithione particles, denotes thoseparticles having a particle size within a range of from about 0.1 toabout 10 microns, and a median particle size of less than 3.0 microns.Preferably the particle size is within a range of from about 0.25 toabout 7 microns, with a median particle size of less than 2 microns.Advantageously, the median particle size of the small size particles iswithin a range of from 0.5 to 3.0 microns, more advantageously within arange of from 0.5 to 2 microns.

The invention also provides a non-dusting composition comprising thesmall particles of pyrithione dispersed in a liquid dispersant,optionally in the presence of one or more dust-inhibiting agents. Thissolid/liquid dispersion is easy to handle, and it reduces or eliminatesthe risk of inhalation exposure of airborne levels of copper pyrithione.Moreover, the small particles of copper pyrithione are physically stablein the dispersion, and in paint, during storage and prior to use. Thisminimizes the likelihood of the formation of copper pyrithione gels orthick thixotropic precipitates, thus providing an enhanced shelf lifefor the dispersions and paints, as compared to dispersions and paintscontaining larger sized particles of copper pyrithione.

As used herein, the term “dispersion” is intended to encompass both lowviscosity solid/liquid mixtures, and higher viscosity solid/liquidcompositions, such as pastes. Generally, the dispersion has a viscosityin the range of from about 1,000 cps to about 100,000 cps at roomtemperature, preferably between about 5,000 cps and 70,000 cps at roomtemperature, wherein “cps” denotes Centipoise. Advantageously, thedispersion comprises from about 20% to about 99.95% (preferably fromabout 20% to about 70%) by weight of small particles of solid copperpyrithione particles dispersed in from about 0.05% to about 80%(preferably from about 30% to about 80%) by weight of a liquiddispersant selected from the group consisting of water, organicsolvents, and combinations thereof. Optionally, the dispersionadditionally contains from about 0.05% to about 30% of a dust-inhibitingagent selected from the group consisting of surfactants, polymer resins,binders, and combinations thereof. All of these weight percents arebased on the total weight of the dispersion.

As used herein, the terms “non-dusting” and “dust-free” refer to acomposition that is substantially free of, advantageously greater thanleast 99% by weight free of, airborne copper pyrithione particles. Theterm “dust-inhibiting agent” refers to compounds that assist inpreventing or inhibiting the formation of dust in the form of airbornecopper pyrithione particles, as compared to a composition that does notcontain those compounds. “Airborne particles” are described in detail inan article entitled “Sampling Criteria for Airborne Particulate Matter”found in the “1999 Threshold Limit Values and Biological ExposureIndices” published by the American Conference of Governmental IndustrialHygienists. That publication states that, for chemical substancespresent in inhaled air as suspensions of solid particles or droplets,the potential hazard associated with airborne particles is a function ofparticle size the relevant particles as well as the mass concentrationof particles.

As noted above, the present invention relates to a compositioncomprising a non-dusting copper pyrithione dispersion of small solidparticles of copper pyrithione dispersed in a liquid dispersant selectedfrom the group consisting of water, organic solvents, and combinationsthereof. Optionally, the dispersion additionally contains adust-inhibiting compound selected from the group consisting ofsurfactants, polymer resins, binders, and combinations thereof. Each ofthese components is described in more detail herein.

Copper pyrithione is available commercially (from Arch Chemicals, Inc.,Norwalk, Conn.) in the form of a dry powder. This form of copperpyrithione may be employed as starting material in the method of thepresent invention.

Alternatively, copper pyrithione may be made by conventional methodsknown in the art, as disclosed in U.S. Pat. Nos. 5,650,095; 5,540,860;5,238,490, all of which are incorporated by reference herein. Briefly,copper pyrithione may be made by reacting a copper salt and/or copperoxide with a pyrithione salt in an aqueous or organic carrier medium.Suitable pyrithione salts are those which are soluble in the organic oraqueous carrier, such as sodium, calcium, potassium, and magnesium saltsof pyrithione, pyrithione acid or the non-metal salts such as theethanolamine salt, chitosan salt, and the disulfide salt of pyrithione(which is commercially available from Arch Chemicals, Inc. as “OMADINEMDS”). The pyrithione salt is preferably employed in an amount ofbetween about 1 and about 40 weight percent, more preferably between 5and 25, and most preferably between about 15 and 25 weight percent, allweight percents being based on the total weight of the reaction mixture,in order to prepare the desired copper pyrithione.

The copper salt used to prepare copper pyrithione is suitably any saltcontaining copper that is soluble in the carrier employed in thereaction. For example, if water is the carrier, useful copper saltsinclude copper chloride dihydrate, copper sulfate, copper carbonate,copper nitrate, copper acetate, as well as combinations thereof. Theabove copper salts may be used individually or in combination, or incombination with copper oxide.

The copper salt, copper oxide and/or copper salt/copper oxidecombination, used to prepare copper pyrithione, is preferably employedin an amount of between about one and about 50 weight percent, morepreferably between 5 and 30 weight percent, and most preferably betweenabout 15 and 20 weight percent, based on the total weight of thereaction mixture.

Carriers that are useful in the reaction mixture for preparing thecopper pyrithione include water, organic solvents, and combinationsthereof. Useful organic solvents include alcohols such as methanol andethanol, amines such as diethanolamine, ethers, esters, and the like.

The non-dusting small particle size copper pyrithione composition isproduced by combining the copper pyrithione, prepared as describedabove, with an aqueous or organic dispersant, and optionallyincorporating a dust-inhibiting agent. The reduction of the particlesize of the copper pyrithione component can occur either prior to,simultaneously with, or after, making the copper pyrithione dispersion.Illustratively, the small particle size copper pyrithione can be madeeither during the manufacturing precipitation of copper pyrithione,prior to the making of the dispersion by milling the dry powder to thedesire size, or during the preparation of the dispersion using a devicethat generates pulverizing forces, such as a mill, to decrease theparticle size of the copper pyrithione particles. As anotheralternative, the particle size of the copper pyrithione particles can bereduced after performing the dispersing step by subjecting thedispersion to pulverizing forces, such as by running it through aparticle size reducing mill. Suitable particle size reducing millsinclude Jet, Air classifying(ACM)), Netzsch, ball, or combination ofsuch mills. As another alternative, equipment that produces pulverizingforces by means of ultrasound, such as sonication devices, may be usedto provide pulverizing forces.

If sonication is used, the sonic energy employed preferably has afrequency of from about 20 Hz to about 250,000 Hz (250 kHz), morepreferably from about 5 kHz to about 105 kHz, and most preferably fromabout 16 kHz to about 20 kHz. Combinations of frequencies may also beused, depending on the configuration of the particular sonicationapparatus. The energy level output that results from the sonic energyapplied to the reaction mixture is preferably in the range from about 20to about 5000 Watts, more preferably from about 100 to about 1000 Watts,and most preferably from about 400 to about 600 Watts. An example of asuitable sonication device suitable for use in the method of theinvention is a Nearfield NAP Model 3606 acoustical processor (availablecommercially from Advanced Sonic Processing Systems, Woodbury, Conn.),although any sonication device may be employed in the method of theinvention.

The copper pyrithione is preferably employed in the dispersion in anamount of between about 20 and 95 weight percent, more preferablybetween about 30 and 70 weight percent, even more preferably betweenabout 30 and 50 weight percent, and most preferably between about 35 andabout 60 weight percent. All weight percents are based upon the totalweight of the dispersion. A particularly useful amount of copperpyrithione is about 45 weight percent.

The optional dust-inhibiting component of the composition of the presentinvention is preferably one or more surfactants, one or more polymerresins, one or more binders, or combinations thereof. If used, thiscomponent generally comprises from about 0.05 to about 30 weight percentof the composition of the invention. If used, the dust inhibiting agentis preferably employed in a total amount of between about 0.05 and about10% by weight, more preferably between 0.1 and about 5% by weight, andmost preferably between about 0.5 and about 2% by weight, all weightpercents being based upon the total weight of the dispersion.

Suitable resins for use as the dust-inhibiting component in thedispersion of the present invention include acrylic resins, vinylresins, alkyd resins, epoxy resins, polyurethane resins, natural resins,rosins, polyester resins, plastisols, and combinations thereof. Vinylresin is particularly useful in the composition of the presentinvention.

Plastisols suitable for use as the dust inhibiting component in thedispersion of the present invention comprise a resin plus a carrier,such as a plasticizer, as described in U.S. Pat. No. 5,319,000, hereinincorporated by reference in its entirety, including commerciallyavailable plastisols containing plasticizers and resin-compatibleadditives. Preferable amounts of the resin component of the plastisolgenerally range from between about 0.2% by weight and about 30% byweight, based upon the total weight of the plastisol.

Binders suitable for use as the dust inhibiting component in thedispersion of the present invention include any low-melt polymer or waxknown in the binding arts. Exemplary binders include rosins such asrosins sold under the trade name “TACOLYN” or “PICOTEX” (hydrocarbonresin monomer produced from co-polymerization of vinyl toluene andalpha-methystyrene), acrylates such as methyl acrylate, ethyl acrylate,and the like, xanthate or guar gums, polyvinyl alcohol, ethyl acetate,and combinations thereof. Useful amounts of the binder componentpreferably range from about 0.1 to about 20 weight percent, morepreferably from about 0.5 to about 10 weight percent, and mostpreferably from about 0.5 to about 5 weight percent, all weight percentsbeing based on the total weight of the composition.

As indicated above, the optional dust-inhibiting agent component of thecomposition of the present invention may be used individually (e.g.,only a surfactant, or only a polymer resin as the dust-inhibitingcomponent). Alternatively, combinations of one or more of theabove-described dust inhibiting agents may be used as thedust-inhibiting component. Moreover, it is possible to employ one ormore of the above-described dust-inhibiting agents (e.g., surfactants)in combination with one or more other dust-inhibiting agents (e.g.,polymer resins) to produce the dust-inhibiting component of the presentinvention.

As indicated above, the copper pyrithione in the dispersion of thepresent invention may take the form of a small particle powder, (e.g., adispersion), or, alternatively, larger non-inhalable granules made up ofsmall particles (e.g., granules greater than 4 microns (4 microns andlarger) Generally, the particle size range for the copper pyrithionepowder commercially available is between about 0.80 micron and about 30microns, with a median particle size between 3 to 6 microns.

In a particularly advantageous dispersion of the present invention, thedust-inhibiting agent is preferably one or more surfactants and/or oneor more polymer resins and/or one or more binders, and the non-dustingsmall particle copper pyrithione dispersion is prepared generally asfollows:

The selected polymer resin and/or surfactant is first added to a mixingvessel and dissolved in the solvent of choice with low speed mixing(generally from about 500-800 rpm) using a high speed disperser type ofmixer well known in the paint and coating art. The copper pyrithionepowder is next added, and the mixing speed is increased to between1,000-3,000 rpm. Mixing is continued until a homogenous dispersion orpaste is produced, generally from about 1 minute to about 30 minutes.Than this dispersion is added to a grinding mill such as a Netzsch ZetaMill and mixed from 10 minutes to 8 hours or until the desired smallparticle size is achieved.

Another method for preparing the small particle copper pyrithionedispersion would be to dry and mill the powder down to a small particlesize first using a jet mill or a air classifying mill that can achievethe desired small particles first. Then this small particle powder isadded to the selected polymer resin and/or surfactant in a mixing vesselwith the solvent of choice and mixed using a high-speed disperser typeof mixer well known in the paint and coating art. The mixing speed isbetween 1,000-5,000 rpm. Mixing is continued until a homogenousdispersion or paste is produced, generally from about 5 minute to about50 minutes.

If copper pyrithione wet filter cake is used to make an organic solventbased dispersion, remaining water must be removed from the finalcomposition. In one embodiment, the above mixing step is done in aclosed flask or reactor with a Dean-Stark trap connection or anotherdevice used for removing the water from the organic solvent. The mixturemay be heated to between about 95° C. to 105° C. or higher until no morewater is being removed from the dispersion. Alternatively, the mixingcan be done under vacuum with lower (or no) required heatingtemperatures. Than this dispersion is added to a grinding mill if neededsuch as a Netzsch Zeta Mill for reduction of particle size and mixedfrom 15 minutes to 5 hours or until the desired small particle size isachieved.

The non-dusting small particle copper pyrithione composition of thepresent invention may be made as a dispersion, which takes the form of athick paste. When made with water as the dispersant, the composition ofthe invention has a viscosity generally in the range of from about 1,000centipoise (cps) to about 75,000 cps at room temperature. Thenon-dusting small particle copper pyrithione composition of the presentinvention made with an organic solvent has a viscosity generally in therange of from about 5,000 cps to about 100,000 cps (preferably 5,000 toabout 70,000 cps) at room temperature.

The non-dusting small particle copper pyrithione composition of thepresent invention offers significant advantages over the copperpyrithione compositions of the prior art. The non-dusting small particlecopper pyrithione compositions of the present invention provide easyprocessing and mixing with paints, coatings, or personal carecompositions, such as soaps, shampoos, medicaments, and the like. Thedust-inhibiting properties of the present invention significantly reducethe presence of airborne copper pyrithione dust in the localenvironment. As a result, the non-dusting small particle copperpyrithione compositions of the present invention can be handled easilywith reduced risk without fear of inhalation of toxic airborne copperpyrithione powder. In addition, it has been found that when the smallparticle copper pyrithione dispersion is spilled and the solventevaporates, the dust-inhibiting component in the dispersion forms a filmon the copper pyrithione, which minimizes dusting. Further, the smallparticles of copper pyrithione seem to stay suspended better indispersions so no thick thixotropic precipitates, and thereforeincreases the shelf life of the present composition.

When added to marine paints this present invention offers significantadvantages over the copper pyrithione compositions of the prior art. Thenon-dusting small particle copper pyrithione compositions of the presentinvention when mixed into a paint, the resulting film coating producedfrom this paint leaches a higher amount of copper pyrithione at thesurface of the coating. This is an advantage because copper pyrithionehas a water solubility of less than 0.50 ppm. In certain marineantifouling paint films if the copper pyrithione does not leach out at ahigh enough concentration marine fouling organisms will settle on thesurface of the film.

Data from the ASTM lab method used to determine the leach rates ofbiocides form marine paint film show that copper pyrithione leach rateis dependent on temperature. The higher the temperature of the water thehigher the leach rate. Upon doing these leach rate test much to thesurprise of the authors the copper pyrithione leach rate was alsodependant on the particle size of the copper pyrithione added to thepaint. The smaller the particle size of copper pyrithione the higher theleach rate of copper pyrithione from the film at all temperaturestested.

EXAMPLES

The invention is further described by the following Examples, but is notintended to be limited by these Examples. All parts and percentages areby weight and all temperatures are in degrees Celsius unless explicitlystated otherwise. All weight percents are based on the total weight ofeach composition, unless explicitly stated otherwise.

Comparative Example A Preparation of a Copper Pyrithione (CuPT)Dispersion in Xylene

As a comparison to the dispersions of the present invention, 13 grams“LAROFLEX MP25” polymer resin (vinyl chloride-isobutyl vinyl ethercopolymer, a product of BASF Corporation, Charlotte, N.C.) was dissolvedinto 832 grams of xylene. Following dissolution of the polymer, 862grams of copper pyrithione (A product of Arch Chemicals ACBV Swords,Ireland) (49% by weight) was added slowly and with constant mixing usinga high speed disperser at a speed of 1000-2000 rpms. The mixture wasstirred at low speed (1000 rpm) and with low shear for 0.5 hours toprovide adequate mixing until a homogenous mixture was achieved. Thecopper pyrithione powder used to make this dispersion was analyzed on aHoriba Laser light scattering particle size analyzer before, and after,it was added to the dispersion and the below data was obtained.

TABLE 1 Median Particle Size Using Commercially Available CopperPyrithione Copper Median Mean Particle Pyrithione Arch Particle SizeSize Chemicals (Microns) (Microns) Before Mixing 3.40 3.09 After Mixing3.36 3.05

As observed from the data in the above table the low shear mixing of thecopper pyrithione powder in the dispersion did not change the particlesize of the copper pyrithione.

Example 1 Preparation of a Small Particle Size Copper PyrithioneDispersion in Xylene

A 300 gram size sample was taken from the dispersion of Example 1, andthe sample was diluted down to a concentration of 42.8% copperpyrithione by adding xylene solvent. The diluted sample was then runthough a Mini Zeta Netzsch mill for 150 minutes at 2000 rpm. Theresulting copper pyrithione dispersion was analyzed on a Horiba Laserlight scattering particle size analyzer and the below data was obtained.

TABLE 2 Median Particle Size Before and After Netzsch Milling A CopperPyrithione Dispersion in Xylene Copper Median Mean Particle PyrithioneDispersion Particle Size Size Arch Chemicals (Microns) (Microns) BeforeNetzsch Milling 3.36 3.05 After Netzsch Milling 0.98 1.06

The Netzsch milled dispersion exhibited better shelf life stability thanthe dispersion made in Example 1.

Example 2

Part A—Preparation of a Small Particle Copper Pyrithione Dispersion inWater

3 grams of “DARVAN” dispersing agent (sodium salt of copoly(naphthalenesulfonic acid/formaldehyde from R.T. Vanderbilt Company, Inc.) wasdispersed into 75 grams of water. Following dissolution of the Darvan,77 grams of copper pyrithione powder was added slowly with continuousmixing using a high-speed disperser (1000-2500 rpms). Stirring wascontinued at low speed (1000 rpms) with low shear to provide adequatemixing until a homogenous mixture is achieved. The dispersion (155 gramstotal) was then milled in a Mini Zeta Netzsch mill for 90 minutes at2000 rpm. The resulting copper pyrithione dispersion was analyzed on aHoriba Laser light scattering particle size analyzer and the below datawas obtained.

TABLE 3 Median Particle Size Before and After Netzsch Milling A CopperPyrithione Dispersion in Water Copper Pyrithione Median Mean ParticleDispersion Particle Size Size Arch Chemicals (Microns) (Microns) BeforeNetzsch Milling 3.80 3.93 After Netzsch Milling 1.84 2.11

Part B—Evaluation of Small Particle Copper Pyrithione Dispersion inMarine Antifouling (“AF”) Paints

Four marine AF paints were made containing the below ingredients:

TABLE 4 Median Particle Size Before and After Netzsch Milling A CopperPyrithione Dispersion in Water Paint Cuprous Oxide Copper Acrylic Number(Wt. %) Pyrithione (%) Polymer (%) 1 40 0 15 2 40 3.0 15 3 40 3.0 15 440 3.0 15

The above four paints were made on a high speed disperser with low shearmixing at 2000 rpm for 30 minutes.

The particle size of copper pyrithione in each paint is described in thebelow table.

Copper Mean Particle Paint Pyrithione Median Particle Size Number UsedSize (Microns) (Microns) 1 None — — 2 Powder 3.40 3.09 3 Example A 3.363.05 Dispersion 4 Example 1 0.98 1.06 Dispersion

The above four paints were applied to cylindrical substrates, allowed todry, and then the painted substrates were placed in tanks with syntheticsea water. The samples are tested following a modified ASTM Leach Ratemethod that is used for copper release rates. The copper pyrithioneconcentration in the synthetic sea water was measured in the AnalyticalDepartment at Arch Chemicals, Inc. using an approved high pressureliquid chromatography (HPLC) method.

The results from the above leach rate comparison testing demonstratethat the small particle copper pyrithione of the present invention hasconsiderably higher leach rate potential at different temperature. Thegraph presented in FIG. 1 depicts a set of curves comparing the leachrate data of the 3 copper pyrithione paints at different watertemperatures. It was observed that the paint containing copperpyrithione having a small particle size within the scope of the presentinvention, namely Paint 4 containing the dispersion of Example 1, had ahigher leach rate, as compared to Paint 3 containing the dispersion ofComparative Example A.

The results presented in FIG. 1 demonstrate that the leach rate ofcopper pyrithione from marine paints varies depending upon the watertemperature to which the marine paint is exposed. When the watertemperature deceases the leach rate decreases significantly. This is anissue because if the water temperature is low it is possible that notenough of copper pyrithione will leach from the paint film to preventmarine fouling.

In FIG. 1, curves 10 and 20 relate to Paint 2 at temperatures 23.5° C.and 10.6° C. respectively. Curves 30 and 40 relate to Paint 3 attemperatures 10.6° C. and 23.5° C. respectively. Curves 50 and 60 relateto Paint 4 at temperatures 23.5° C. and 10.6° C. respectively.

The results presented in FIG. 1 also demonstrate that the copperpyrithione leach rate from the marine paints was also dependent on theparticle size of the copper pyrithione added to the paint.Advantageously, the small size particles of copper pyrithione containedin Paint 4 provided a significantly higher leach rate, as compared tothat provided by the larger size particles contained in Paint 3,particularly at the low water temperature of 10.6 degrees Centigrade.The higher leach rate of the copper pyrithione from Example 1 (Paint 4),as compared to that from Comparative Example A (Paint 3), indicates thatthe Example 1 dispersion will provide enhanced antifouling efficacy inpaint, as compared to the antifouling efficacy provided by thedispersion of Comparative Example A.

Example 3 (Proposed Cold Water Exposure)

The four marine AF paints prepared in Part B of Example 2 are tested forantifouling efficacy using the following protocol:

A sample of each of the four paints is painted onto fiberglass panelshaving dimensions of 6 inches by 16 inches. The four coated panels aresubmerged in ocean water off the coast of Main. (Portland) for a periodof 5 months in order to provide a basis for comparing the antifoulingefficacy of the paints in a cold water environment. The ocean watertemperature varied from 6 degrees C. to 17 degrees C. during the periodof the test, with the average water temperature being 11 degrees C.

After the test period, the four-coated panels are removed from the oceanwater, and visually examined for barnacle and microorganism growth. Theresults of this examination provide the following comparative table.

Five-month exposure Data:

Paint Cuprous Oxide Copper Total Fouling Number (Wt. %) Pyrithione (%)on panel (%) 1 40 0 85 2 40 3.0 75 3 40 3.0 75 4 40 3.0 5

The results of the comparison confirm the enhanced antifouling efficacyof the copper pyrithione from Example 1 (Paint 4), as compared to thatfrom Comparative Example A (Paint 3).

While the invention has been described in combination with embodimentsthereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andbroad scope of the appended claims. All patent applications, patents,and other publications cited herein are incorporated by reference intheir entireties.

What is claimed is:
 1. A composition comprising small particles ofcopper pyrithione having a particle size within a range of from about0.1 to about 10 microns, and a median particle size of from 0.5 to 3.0microns, said small particles exhibiting enhanced antimicrobialperformance, as compared to larger size copper pyrithione particles, ina marine paint that is exposed to a cold water environment of from about5 degrees Centigrade to about 15 degrees Centigrade, said smallparticles of copper pyrithione exhibiting a leach rate of at least onemicrogram per square centimeter per day based on exposure of said paintto said cold water environment.
 2. A paint containing the composition ofclaim 1 in an antifouling effective amount of from about one percent toabout 5 percent based upon the total weight of the paint.
 3. A methodfor enhancing the antifouling efficacy of a paint in a cold waterenvironment, said method comprising incorporating the composition ofclaim 1 into the paint.
 4. A composition comprising a non-dusting copperpyrithione dispersion comprising small solid particles of copperpyrithione dispersed in a liquid dispersant, said solid particles havinga particle size within a range of from about 0.1 to about 10 microns anda median particle size of from 0.5 to 3.0 microns.
 5. The composition ofclaim 4 wherein said solid particles have a particle size within a rangeof from about 0.25 to about 7 microns and a median particle size of from0.5 to 2 microns.
 6. The composition of claim 4 wherein said solidparticles have a median particle size within a range of from about 0.5to about 2.8 microns.
 7. The composition of claim 4 wherein said liquiddispersant is selected from the group consisting of water, organicsolvents, and combinations thereof.
 8. The composition of claim 4wherein said solid particles are present in an amount of from about 20%to about 99.95% by weight, and said liquid dispersant is present in anamount of from about 0.05% to about 80% by weight, based upon the totalweight of the composition.
 9. The composition of claim 4 wherein saidsolid particles are present in an amount of from about 20% to about 70%by weight, and said liquid dispersant is present in an amount of fromabout 30% to about 80% by weight, based upon the total weight of thecomposition.
 10. A composition comprising a non-dusting copperpyrithione dispersion comprising small solid particles of copperpyrithione dispersed in a liquid dispersant, said solid particles havinga particle size within a range of from about 0.1 to about 10 microns anda median particle size of from 0.5 to 3.0 microns, wherein said solidparticles are present in an amount of from about 20% to about 70% byweight, and said liquid dispersant is present in an amount of from about30% to about 80% by weight, based upon the total weight of thecomposition, wherein the composition additionally contains from about0.05% to about 30%, based upon the total weight of the dispersion, of adust-inhibiting agent selected from the group consisting of surfactants,polymer resins, binders, and combinations thereof.
 11. A method ofmaking a non-dusting dispersion of small solid particles of copperpyrithione dispersed in a liquid dispersant comprising the steps of: (a)providing small solid particles of copper pyrithione within a size rangeof from about 0.1 to about 10 microns, and a median particle size offrom 0.5 to 3.0 microns, by subjecting larger solid particles of copperpyrithione to a force selected from the group consisting of grinding,milling, pulverizing, sonicating, and combinations thereof, and (b)dispersing said small copper pyrithione particles in a liquiddispersant.
 12. The method of claim 11 wherein said milling is effectedby a technique selected from the group consisting of ball milling, jetmilling, air classifying milling (ACM), Netzsch milling, andcombinations thereof.
 13. A method of making a non-dusting dispersion ofsmall solid particles of copper pyrithione dispersed in a liquiddispersant comprising the steps of: (a) dispersing larger solidparticles of copper pyrithione in a liquid dispersant to provide aliquid dispersion have said larger solid particles dispersed therein,and (b) subjecting said liquid dispersion of copper pyrithione to aforce selected from the group consisting of grinding, milling,pulverizing, sonicating, and combinations thereof, in order to reducethe size of said larger size particles in said dispersion within a sizerange of from about 0.1 to about 10 microns, and a median particle sizeof from 0.5 to 3.0 microns.
 14. The method of claim 13 wherein saidmilling is effected by a technique selected from the group consisting ofball milling, jet milling, air classifying milling (ACM), Netzschmilling, and combinations thereof.
 15. A method of enhancing theantifouling characteristics of a paint which comprises adding to thepaint an antifouling effective amount of solid particles of copperpyrithione having a particle size within a range of from about 0.1 toabout 10 microns and a median particle size of from 0.5 to 3.0 microns.16. The method of claim 15 wherein the solid particles of copperpyrithione have a particle size within a range of from about 0.25 toabout 7 microns and a median particle size of from 0.5 to 2 microns. 17.An antifouling paint comprising a paint base and an antifoulingeffective amount solid particles of copper pyrithione having a particlesize within a range of from about 0.1 to about 10 microns and a medianparticle size of from 0.5 to 3.0 microns.
 18. An antifouling paintcomprising a paint base and an antifouling effective amount solidparticles of copper pyrithione having a particle size within a range offrom about 0.25 to about 7 microns and a median particle size of from0.5 to 2 microns.
 19. A method of enhancing, in a cold water marineenvironment, the leach rate of copper pyrithione from a copperpyrithione-containing paint, said method comprising incorporating intothe paint solid particles of copper pyrithione having a particle sizewithin a range of from about 0.1 to about 10 microns and a medianparticle size of from 0.5 to 3.0 microns, in order to provide a copperpyrithione leach rate from the paint of at least one microgram persquare centimeter per day of exposure of said paint to said cold watermarine environment when measured at a cold water temperature of 10.6degrees Centigrade.
 20. The method of claim 19 wherein said copperpyrithione is present in an antifouling effective amount of anon-dusting copper pyrithione dispersion comprising small solidparticles of copper pyrithione dispersed in a liquid dispersant, saidsolid particles having a particle size within a range of from about 0.1to about 10 microns and a median particle size of from 0.5 to less than3.0 microns.
 21. The method of claim 19 wherein the compositionadditionally contains from about 0.05% to about 30%, based upon thetotal weight of the dispersion, of a dust-inhibiting agent selected fromthe group consisting of surfactants, polymer resins, binders, andcombinations thereof.
 22. A copper pyrithione-containing antifoulingpaint providing an enhanced rate of leaching of the copper pyrithionefrom the paint in a cold water marine environment, said paint comprisinga paint base and an antifouling effective amount of solid particles ofthe copper pyrithione, said solid particles having a particle sizewithin a range of from about 0.1 to about 10 microns, and a medianparticle size of from 0.5 to 3.0 microns, said solid particles having aleach rate from the paint of at least one microgram per squarecentimeter per day of exposure of said paint to said cold water marineenvironment when measured at a cold water temperature of 10.6 degreesCentigrade.
 23. The copper pyrithione-containing antifouling paint ofclaim 22 wherein said copper pyrithione is present in an antifoulingeffective amount of a non-dusting copper pyrithione dispersioncomprising small solid particles of copper pyrithione dispersed in aliquid dispersant, said solid particles having a particle size within arange of from about 0.1 to about 10 microns and a median particle sizeof from 0.5 to 3.0 microns.
 24. The copper pyrithione-containingantifouling paint of claim 22 wherein said dispersion additionallycontains from about 0.05% to about 30%, based upon the total weight ofthe dispersion, of a dust-inhibiting agent selected from the groupconsisting of surfactants, polymer resins, binders, and combinationsthereof.